1. Field of the Invention
The present invention relates to a nozzle plate, a method of manufacturing a nozzle plate, a liquid droplet ejection head, a method of manufacturing a liquid droplet ejection head, and an image forming apparatus, and more particularly, to a nozzle plate, a method of manufacturing a nozzle plate, a liquid droplet ejection head, a method of manufacturing a liquid droplet ejection head, and an image forming apparatus suitable for a recording head (print head) which ejects liquid from a nozzle.
2. Description of the Related Art
Image forming apparatuses such as inkjet printers use a liquid droplet ejection head comprising nozzles (nozzle holes) which eject liquid onto an ejection receiving medium, such as paper, pressure chambers connected to the nozzles, and pressurization devices (actuators such as piezoelectric elements) for pressurizing the liquid inside the pressure chambers.
In a liquid droplet ejection head, since liquid is ejected from the nozzles in the form of liquid droplets, the surface properties of the liquid droplet ejection side of the nozzle forming surface of the nozzle plate in which the nozzles are formed (in other words, the surface on the side of the nozzle plate adjacent to the ejection receiving medium, which is also called the “nozzle forming surface” below), have a great influence on the liquid droplet ejection characteristics. For example, if ink adheres to the peripheral regions of the nozzles, then not only does the liquid droplet ejection direction become unstable, but other problems may also arise, such as decrease of the nozzle diameter, reduction of the liquid droplet ejection amount (reduction of the size of the liquid droplets), fluctuation of the liquid droplet ejection speed, and so on. Therefore, technology is known in which a liquid-repellency film (liquid-repellency layer, lyophobic film) is formed on the surface of the nozzle forming surface, thereby preventing adherence of ink to the peripheral regions of the nozzles and hence improving liquid droplet ejection characteristics.
For this liquid-repellency layer, technology is generally used in which an organic thin film having added fluorine, or a fluorine-based lyophobic agent is coated onto the nozzle forming surface, in particular with the object of providing functions for “wear resistance” and “liquid-repellency for stabilizing flight”. Furthermore, technology for forming a non-organic thin film with added fluorine is also known. However, if such a nozzle forming surface is used for a long period of time, or wiped repeatedly, or the like, the fluorine is removed and the liquid-repellency layer degrades, thereby reducing the liquid droplet ejection characteristics.
In order to resolve this, Japanese Patent Application Publication No. 2004-276568 discloses a nozzle forming surface where detachment of the liquid-repellency layer is prevented by forming a thin film layer made of diamond-like carbon (DLC) having excellent adhesive properties with respect to the nozzle plate, and a DLC layer with added fluorine is formed as a liquid-repellency layer so that liquid-repellency is imparted to the nozzle forming surface. The DLC layer with added fluorine in Japanese Patent Application Publication No. 2004-276568 has two or more layers of different added amounts of fluorine, whereby the added amount of fluorine is reduced on the layer adjacent to the DLC, and the added amount of fluorine is increased, the nearer the position to the surface. Thereby, good liquid-repellency is achieved, and even if a certain amount of fluorine becomes detached from the layer where the added amount of fluorine is larger at the surface, then since there is a large added amount of fluorine, it is possible to maintain the liquid-repellency.
DLC is a general term for a carbon thin film which are synthesized by vapor phase synthesis using ions, or the like, and which has properties similar to those of diamond, for example, high hardness, electrical insulating properties, infrared transmissivity, and the like. Therefore, the liquid-repellency layer described in Japanese Patent Application Publication No. 2004-276568 is strongly resistant to shocks caused by rubbing during wiping, or the like, but it is liable to suffer cracking or chipping in response to any mechanical impacts that may arise during paper jams, maintenance operations, or the like.
Furthermore, if there is a difference in the coefficient of linear expansion between the flow channel substrate (namely, the plate having ink flow channels comprising pressure chambers and the like) which is attached to the nozzle plate, and the nozzle plate itself, then a tensile stress or compressive stress arises between the flow channel substrate and the nozzle plate when the temperature rises during manufacturing, for example, and hence bending of the nozzle plate may occur. Moreover, if the material of the nozzle plate is an organic film, such as polyimide, then the organic film itself swells due to absorption of the ink, and the nozzle plate may suffer bending. Consequently, there is a possibility that the DLC may break off from the surface of the nozzle plate.